1. Field of the Invention
An embodiment of the disclosure relates to a receiving device and a receiving method.
2. Description of the Related Art
In recent years, broadcast signals used in digital television broadcasting conform to OFDM (Orthogonal Frequency Division Multiplexing) scheme. The OFDM scheme is a technique of effectively transmitting data using a limited frequency band by transmitting effective symbols including broadcast content in a parallel way through a plurality of carriers having phases orthogonal to each other.
A receiving device that receives a broadcast signal according to the OFDM scheme acquires a symbol corresponding to data from the broadcast signal by performing FFT (fast Fourier transform) on the received broadcast signal, and reproduces broadcast content by performing OFDM demodulation on the acquired symbol.
Meanwhile, a broadcasting station that transmits a broadcast signal according to the OFDM scheme adds a guard interval copied from a tail part of each effective symbol to a head part of each effective symbol and then transmits each symbol in order to improve immunity to a multipath delay.
As described above, the same data (symbol) as a part of an effective symbol is included in the guard interval. Based on this, a technique of improving a receiving characteristic by synthesizing the guard interval with the effective symbol has been proposed.
For example, a receiving device disclosed in JP2000-151542A improves a receiving characteristic by delaying a guard interval by a time corresponding to the duration of an effective symbol and then adding/synthesizing the guard interval to/with a tail part of an effective symbol before performing FFT on a received broadcast signal.
Meanwhile, in a receiving device for a vehicle, when a broadcast signal is received during high-speed movement, orthogonality of a carrier collapses due to Doppler shift, causing inter-carrier interference. When the inter-carrier interference occurs, it is difficult for the receiving device to acquire a valid symbol, and thus a receiving characteristic degrades.
For this reason, for example, a receiving device improves a receiving characteristic by calculating the ICI based on a time variation of a transmission channel response of a received broadcast signal and then removing the ICI from the broadcast signal.
Specifically, the receiving device acquires an SP (scattered pilot) signal from the broadcast signal which has been subjected to the FFT. Then, based on the acquired SP signal, the receiving device estimates an original transmission channel response of the broadcast signal and estimates a time variation of the transmission channel response of the received broadcast signal.
Then, the receiving device calculates the ICI based on a difference between the estimated original transmission channel response of the broadcast signal and the time variation of the actual transmission channel response, and removes the calculated the ICI from the broadcast signal, thereby improving the receiving characteristic.
However, when the technique (hereinafter, referred to as a “guard adding technique”) of adding/synthesizing the guard interval to/with the effective symbol is used together with the technique of removing the ICI, the calculation accuracy of the ICI is lowered.
Specifically, in the guard adding technique, when the guard interval is synthesized with the effective symbol, the guard interval is delayed by a time corresponding to the duration of the effective symbol and then synthesized with the effective symbol before the FFT is performed.
However, in the technique of removing the ICI, the ICI is calculated based on the FFT-processed broadcast signal, and influence caused by delaying the guard interval before the FFT is performed is reflected in the time variation of the transmission channel response used to calculate the ICI.
For this reason, when the guard adding technique is used together with the technique of removing the ICI, it is difficult to accurately calculate a time variation related to the transmission channel response of the received broadcast signal, whereby the calculation accuracy of the ICI is lowered.
Thus, how to implement a receiving device and a receiving method which are capable of improving the calculation accuracy of the ICI while using the guard adding technique together with the technique of removing the ICI has become a big issue.